Polyolefins are used in a variety of diverse applications. For example, such applications include food packaging, electronic components, automobile parts, fibers and fabrics, and medical equipment. Polyolefins could not perform such diverse functions without the assistance of a very broad range of additives. Without additives, polyolefins can degrade during processing and over time can lose impact strength, discolor, and become statically charged. Additives not only overcome these and other limitations, but also can impart improved performance properties to a final polyolefin product. One type of additive is antioxidants which usually are used to retard the degradation of polymers.
Degradation can be initiated when free radicals, highly reactive species with an unpaired electron, are created in polyolefins by heat, ultraviolet radiation, mechanical shear, or metallic impurities. It is believed when a free radical is formed, a chain reaction can begin that initiates oxidation of the polyolefin component. Subsequent reaction of the radical with an oxygen molecule can yield a peroxy radical, which then can react with an available hydrogen atom to form an unstable hydroperoxide and another free radical. In the absence of an antioxidant, these reactions can become self-propagating and can lead to degradation.
There are two basic types of antioxidants, primary and secondary antioxidants. It is believed that primary antioxidants can intercept and stabilize free radicals by donating active hydrogen atoms. It also is believed that secondary antioxidants can prevent formation of additional free radicals by decomposing unstable hydroperoxides into a stable product. When primary antioxidants, such as hindered phenols, are utilized, polyolefins can have a more yellow color than unstabilized polyolefins, therefore decreasing the commercial value of the polyolefins. Secondary antioxidants, such as phosphite compounds, often are utilized to increase the stability and whiteness of polyolefins.
Bis(2,4-dicumylphenyl)pentaerythritol diphosphite is a secondary antioxidant that provides excellent resistance against polyolefin degradation. However, when the polyolefin component containing bis(2,4-dicumylphenyl)pentaerythritol diphosphite is exposed to high temperature and humidity, as much as 80% of the bis(2,4-dicumylphenyl)pentaerythritol diphosphite can degrade over a period of twelve weeks. For example, these conditions can occur when a polyolefin component is transported from a polyolefin polymerization facility to a facility where the polyolefin component is used to make various products.
There is a need in the industry to provide a process for producing a polyolefin composition comprising at least one polyolefin component produced from a transition metal halide catalyst and bis(2,4-dicumylphenyl)pentaerythritol diphosphite where the bis(2,4-dicumylphenyl)pentaerythritol diphosphite does not degrade as quickly in the polyolefin composition.